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Study and Diagnosis of Disease > Lecture 04 - Eukaryotic Translation > Flashcards

Lecture 04 - Eukaryotic Translation Flashcards

1
Q

What are proteins

A

the mini tools/molecular machines that carry out what we term functions in the cell

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2
Q

How much of a mammalians cell energy is used for protein translation

A

30%

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3
Q

What are the four major stages of protein translation

A
  1. load amino acids onto tRNAs
  2. Initiation
  3. Elongation
  4. Termination
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4
Q

Why do tRNAs, elongation factors and termination factors all have similar structures

A

because they all need to fit in to the A-site

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5
Q

Why is translation initiation more complex in eukaryotes than prokaryotes

A

it requires more regulation

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6
Q

How many and what initiation factors are required for prokaryotic initiation

A

three
IF1, IF2, IF3

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7
Q

How many and what initiation factors are required for eukaryotic initiation

A

nine
eIF1, 2, 3, 4A, 4B, 4C, 4D, 5, 6

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8
Q

What are the four complexes of intitiation

A
  1. 43S pre-initiation complex
  2. eIF4-mRNA complex
  3. 48S initiation complex
  4. 80s elongation complex
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9
Q

What occurs during the 43S pre-initiation complex

A

the complex is put together mRNA

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10
Q

What occurs during the eIF4-mRNA complex

A

mRNA is prepped so that it is positioned properly when it binds the 43C PIC

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11
Q

What occurs during the 48S initiation complex

A

the ribosome binds to the mRNA and scans for the start codon

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12
Q

What occurs during the 80S elongation complex

A

60S is bring in to start elongation

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13
Q

What components make up the 43S pre-initiation complex

A

40S ribosomal subunit, eIF1 and eIF1A, eIF2-GTP-Met-tRNA, eIF3, eIF5

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14
Q

What is step one of the 43S pre-initiation complex

A

prepping the ribosome

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15
Q

How is the ribosome prepped

A

binding of eIF1 and eIF1A causes a conformational change that opens up the channel allowing mRNA access as well as blocking the A and E sites from tRNAs

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16
Q

What site does eIF1A bind to

A

the A site

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17
Q

What site does eIF1 bind to

A

the E site

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18
Q

What is the purpose of the eIF2 ternary complex

A

it delivers the Methionine initiator to the 40S subunit

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19
Q

What is eIF2B

A

a quanine exchange factor that triggers the reloading of eIF2 with Methionine initiator

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20
Q

What is unique about the methionine initiator

A

it is structurally different than methionine elongator, they cannot be interchanged, low levels of the initiator reduces translation (regulatory)

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21
Q

What is eIF3

A

the largest initiation factor (13 subunits), it is used to stabilize the 43S PIC and shields the entry and exit

22
Q

What is eIF5

A

a GTPase activating protein that activated eLF2, it is usually blocked to prevent premature hydrolysis of the GTP

23
Q

What is a UTR

A

untranslated region

24
Q

What is the purpose of a 5’UTR

A

regulation of translation

25
Q

Where is a UTR

A

after the 5’ cap and before the Poly-A-tail

26
Q

What are the three parts of eIF4

A

eIF4A, eIF4E, eIF4G

27
Q

What is eIF4A

A

an RNA helicase that unwinds the mRNA hairpin

28
Q

What is eIF4E

A

a cap binding protein

29
Q

What is eIF4G

A

the scaffold that binds eIF3 and the polA binding protein

30
Q

What is eIF4B

A

a factor that enhances the helicase activity of eIF4A

31
Q

What is eIF4 used for

A

the circulation of mRNA

32
Q

How does eIF4 cause the circulation of mRNA

A

eIF4G binds both eIF4E and polyA binding protein which leads to the circularization

33
Q

How is mRNA recruited onto the 43S ribosome subunit

A

eIF4G interacts with eIF3 (on the ribosome) and eIF4E (the cap binding protein attached to the mRNA)

34
Q

How does the ribosome find the initiation site

A

after binding at the 5’ cap it then scans from 5’ to 3’ along the 5’UTR to find the AUG start codon, this must fall into the P-site

35
Q

What is the Kozak Consensus Sequence

A

a sequence prior to the start codon that tells the ribosome that the start codon is near

36
Q

What are the bases in the Kozak Consensus Sequence

A

GCCRCC(AUG)G

R= either A or G

37
Q

What does it mean if translation is polycistronic

A

a weak Kozak Consensus can cause the 48S to scan past the AUG site to the next site causing a different protein to be made from the same mRNA

38
Q

What is eIF5B

A

a GTPase that mediate the joining of the 60S and 40S subunits

39
Q

What change occurs to prep for the addition of the 60S subunit

A

eIF1 is kicked out during initiation which allows eIF5 to contact eIF2 which hydrolyzes GTP to GDP (it can no longer hold the mRNA in place)

40
Q

What happens as the 60S subunit binds

A

the eIFs bound to the 40S subunit dissociate away

41
Q

What eIF stays bound and why

A

eIF1A remains bound and acts as a docking site for eIF5B

42
Q

How does elongation begin

A

60S subunit stimulates the GTP hydrolysis of eIF5B which dissociates along with eIF1A, the ribosome can now move along the mRNA

43
Q

How can viruses trick the translation system

A

fake cap making proteins, cutting caps off host mRNA, hijacking the cap making machinery, structural changes

44
Q

What is a specific example of a virus tricking the translation system

A

a type IV virus that uses its RNA to shape like a tRNA, tricks the system into thinking there is something in the P site and triggers translation

45
Q

How can a virus modify the 40S subunit

A

it can use its RNA shape to open the mRNA channel without the use of initiation factors

46
Q

What are the steps of elongation

A
  1. eEF1 brings tRNA to the A site, iif the tRNA anticodon matches GTP is hydrolyzed to GDP leaving the tRNA in the A-site
  2. peptide bond is formed between amino acid and growing chain
  3. eEF2 fits into the A site and when hydrolyzed slides the ribosome over 3 nucleotides, the now empty tRNA in the E site diffuses away, cycle continues
47
Q

What are the steps of termination

A
  1. eRF1-eRF3 binds to the stop codon
  2. eRF3 is hydrolyzed and breaks off
  3. energy is used to kick eRF1 further into the A site which initiates a fake amino transferase
  4. sometimes the polypeptide just falls off, if not ABCE1 helps kick it off
  5. ABCE1 pulls apart the subunits by further wedging in eRF1 and acts as a block so the subunits cannot reaggregate
48
Q

Why do many antibiotics target both prokaryotic and eukaryotic ribosomes

A

they are similar in structure and function, since the process of translation is so energy draining it is evolutionary conserved if there are big changes made the system will not work

49
Q

Why do tetracyclines only inhibit prokaryotic translation

A

it tends to bind to the outer edges of the ribosome which have more ability to change causing more differences between prokaryotic and eukaryotic

50
Q

How do tetracyclines work

A

binds to the small subunit and blocks tRNAs from entering the A site

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